Method to Estimate the Physical and Mental Workloads due to Motorcycle Riding Using R-R Interval Variability of Electrocardiogram

A method to evaluate rider's mental and physical workloads (MPWL) using R-R interval (RRI) was studied and proposed. The RRI of 4 subjects riding a motorcycle over 400 km was measured and compared with that of the non-riding day, and the relation with MPWL based on subjective evaluation was discussed. While the average RRI of 5 minutes duration, defined as RRM, is a statistic which would reflect MPWL, the effect of circadian rhythm is not negligible, and therefore RRM in long-term riding should be adjusted by the RRM in the non-riding day so as to reflect the rider's MPWL more clearly. The standard deviation of RRI reflects not only short-term RRI variability but also trend of RRI caused by transient change in tension. Thus, it is not suitable for describing tonic states such as rider's MPWL which is reflected by short-term RRI variability. To obtain a more robust statistic in relation to this variability, a new statistic named RRV15 was introduced. RRV15 is a statistic which would reflect tonic states, but the tonic states itself could show circadian rhythm, and so it is not possible to estimate pure MPWL directly from RRV15 itself. There was a remarkable tendency during the riding lest for RRV15 to gradually decrease while riding and to recover quickly while taking a rest. Accordingly, a new statistic, RER, referred to as the Recovery Ratio, was defined to quantify recovery performance from the MPWL due to riding. This was an attempt to estimate the MPWL level from recovery performance in RRV15. and was confirmed to agree quite well with the subjective evaluation of MPWL in riding. This method does not require compensation with the non-riding day, and is believed to be practical and useful in evaluation the actual MPWL level in practical circumstances such as operating a vehicle.